Thermal time delay relay



Nov. 4, 1958 A. L. BASTIAN THERMAL TIME DELAY RELAY Filed Jan. 10, 1957\k m i INVENTOR. ARTHUR L. EAETIAN Hi5 ATTORNEY States THERMAL TIMEDELAY RELAY Arthur L. Bastian, Yonkers, N. Y., assignor to Curtiss-Wright Corporation, a corporation of Delaware This invention relates tothermal time delay relays of the kind in which a bimetallic elementresponsive to a heater actuates a switching member, and in which asecond bimetallic member is employed to compensate for ambienttemperature changes.

Thermal time delay relays of the character described have been found tovary considerably in time delay operation even though of apparentlyidentical construction. As a given relay is cycled through its intendedambient temperature range, hysteresis effects have been observed; i. e.the time delay at a given ambient temperature has been found to benon-repeatable, as where the relay is first tested at an initial ambienttemperature, next at a different ambient temperature and again at theinitial ambient temperature, n xt at a different ambient temperature andagain at the initial ambient temperature.

'It is an object of the invention to provide an improved relay structurewhich is effective in minimizing hysteresis effects.

Another object of the invention is to provide an improved relaystructure effective to minimize response variations from relay to relay.

In general bimetal strips are subject to two warping effects. Theprincipal and desired effect takes place about an axis transverse to themajor longitudinal axis'of the strip and results in a cantilever orspiral deformation responsive to temperature changes. The'second andunclesired warping effect takes place about the longitudinal axis of thebimetal and results in a cross-bowing deformation. The two eifects areinterdependent as increased cross-bowing results in reduced bimetalactivity, i. e. reduced principal cantilever deformation. In relaysheretofore known the securing means have been depended on to determineboth the fulcrum line for the principal Warping effect of the bimetalmember and also to restrain cross-bowing. The extent of cross-bowingrestraint had depended largely on the amount of stress due to theclamping action of the securing means and had varied radically owing todifferences in clamping force and also due to imperfections in thesecuring means. Because of the aforementioned interdependence of thewarping effect the extent of desired warping of the unsecured active'portion of the bimetal has likewise varied considerably anduncontrollably so. Moreover the securing means have not provided aclearly defin d fulcrum line for the principal warping of the bimetalmember from relay to relay or even for a given relay with temperaturecycling.

In accordance with the invention the bimetal strips are supported incantilever fashion, but the secured end portions thereof are precludedfrom warping in the principal direction and also from cross-bowing inthe transverse direction. This is accomplished by providing the securedportions with a pair of flanges which preclude cantilever deflection ofthe secured end portion. Moreover the ends of the flanges are disposedin a common plane extending transversely of the longitudinal extensionof the bimetal member and this plane positively establishes a uniformand invariant fulcrum line'for the principal warpingof atent C ice themember. The portion immediately adjacent to the secured end portion isoff set relative to the secured end portion and also to the major activeportion and thus precludes cross-bowing of the secured portion.

For a better understanding of the invention, reference may be had to thefollowing more detailed description considered together with theaccompanying drawing in which like characters identify like parts and inwhich Fig. l is a perspective view of a relay embodying the invention,the relay being enclosed in an envelope shown partially broken away;Fig. 2 is an elevational view of the relay shown in Fig. 1 with theenvelope omitted; Fig. 3 is a partly fragmentary front elevational viewof the lower terminal portions of the bimetallic members in Figs. 1 and2; Fig. 4 is a sectional view taken along the line ;4 in Fig. 3; Fig. 5is a partly fragmentary enlarged. perspective view of the yoke andcompensator bimetallic member generally shown as in' Fig. 1 butseparated for convenience in illustration; and Fig. 6 is a diagrammaticrepre sentation of the relay circuitry.

As shown in Fig. 1 the relay structure 12 is enclosed in an envelopeconsisting of a metallic base member 1a and a metallic cover member 16.The base 14 includes a circular disc portion 18 and a concentriccircular portion 20 of somewhat larger diameter shouldered on disc Thecover 16 is generally in the form of a thin walled circular cylindercoaxial with the base and has a closing upper end wall 22, Whereas itslower end is open to engage the base member 14. The outside of cover 16is formed to a concave inward ring 23 towards the lower end thereof andthe corresponding inner convex surface 24 is intended to snap over theshoulder 26 onto the disc member 18 for tight fitting engagementtherewith and also with the shoulder 20. The envelope may be evacuatedor filled with a gas, in which case first the junction of base 14 andcover 16 is hermetically sealed off by welding or soldering; next avacuum or gas line is introduced through an opening in the wall 22, andfinally the opening is sealed off as indicated at 25, also by welding orsoldering.

The relay is intended to plug into a standard 7 pin miniature tubesocket and to this end there are provided seven relatively rigid contactpins, numbered sequentially from 1 to 7 in a counterclockwise directionas viewed from above the base, and extending downwardly of the base 14in spaced relation to one another. Referring to Fig. 6, in which thepins are numbered in the conventional clockwise sequence as viewed frombelow the base, the No. 1 pin is connected to the normally closedcontact 26 by means of the connections 28. A heater winding 30 isconnected across the Nos. 2 and 3 pins to which heater power from asuitable source may be applied. The No. 5 pin by means of the connection31 is connected to an armature 32 to whose opposite sides contacts 34and 36 (Fig. 2) are secured. Contact 36 normally makes a connection withthe fixed contact 26 whereas contact 34 is intended upon heating of theheater 36 to make a connection to another fixed contact 38 which isconnected to the No. 7 pin. The Nos. 4 and 6 pins are not usedelectrically. The relay may be operated as a single pole double throwswitch by introducing a current at pin 1 and passing the currentnormally through pin 5 and alternately (when heater 30 is heated)through pin 7. The relay may also be operated as single pole normallyclosed by passing a current normally between pin 1 and pin 5. The relaymay also be operated as single pole normally open, in which case circuitconnections are brought to the N0. 1 and No. 7 pins.

Referring to Fig. 2, pin 1 is structurally typical of all other pinsexcept the Nos. 4- and 6 pins. It comprises a vertical portion 1a whichextends from below the base 14, through an aperture in the base 14 andthen above 3 the base 14 to the interior of the envelope. An insulatingfiller 39 (Fig. 1) seals the aperture and spaces the pin 1 from the base14. In the interior of the envelope the pin 1 is bent inwardly as at 40and then bent once moreto vertical alignment so as to form an endportion 42. The end portion 42 is welded to the front end of a metallicbar 44. 7 Bar 44 extends in parallel relation to an axial sectionalplane (not shown) passing approximately mid-way between the No. 1 andNo. 7 pins. The bar 44 is integrally formed with the fixed contact 26which is approximately centered thereon and projects upwardly thereof.The Nos. 4 and 6 pins are provided solely for engagement in the matingmembers of the tube socket and for this reason they may be clipped offabove the base 14 as shown. Otherwise they are structurally similar tothe other pins. The internally off-set structure of the pins serves tospace the relay structure 12 apart from and above the base 14 and alsoto support the relay structure 12 in fixed spatial disposition.

The relay structure 12 proper is arranged in a stacked assembly whichcomprises in order the following elements (Figs. 1 and 2); thecompensator bimetal 48; a metallic strip 49; an annular insulating,spacing, and supporting member 50; a metallic bar 52; a similar annu larinsulating, spacing, and supporting member 54; the aforesaid bar 44; astill third annular insulating, spacing, and supporting member 56; andthe actuator bimetallic member 58.

The lower ends of each of the stacked elements are disposed insubstantially a common plane parallel to the base 14. The elementsextend upward of the common plane in substantially parallel relation toone another with adjacent elements in mechanical contact and flush andclamping relation. The mechanical contact is assured by means of afastening screw 60 which extends through apertures in the bars, thebimetallic members, and insulating spacers, and a therewith engaged nut61 located on the outside of the compensator 48. The'apertures in thebars 44 and 52 are sufliciently large to preclude contact with screw 60and short-circuiting thereto. The strip 49 is welded onto the upper endof the No. pin. The bar 52 in a fashion similar to that of bar 44includes the fixed normally open contact 38 and is welded onto the upperend of the No. 7 pin. The bimetallic members 48 and 58 are ofsubstantially rectangular strip form and extend upwardly of their fixedlower ends. They are arranged to Warp in a counterclockwise directionresponsive to a temperature increase and in a clockwise directionresponsive to a temperature decrease.

In accordance with the invention the secured portions of the bimetallicmembers 48 and 58 and also the portions thereof immediately adjacent tothe secured portions are deliberately deformed for positive definitionof fulcrum lines. Referring to Figs. 3 and 4 each of 'the bimetallicmembers has an end portion 100 provided with an aperture 102 throughwhich the screw 60 passes. The end portion terminates in a sharplydefined line 103 which also marks the beginning of a relatively shortintermediate portion 104 which extends obliquely and in oft"- setrelation to the end portion 100. Portion 104 terminates at a secondsharply defined line 105 which also marks the beginning of the mainactive portion 106 of the bimetal member. Portion 106 extends upwardlyof the stacked assembly and in parallel and ofi-set relation to the endportion 100. The arrangement is such that the central portions 104extend laterally inwardly toward the center of the relay structure sothat the active portions 106 are nearest to one another and the endportions 100 are farthest from one another. p

The intermediate portion 104 is of narrower width than the main activeportion 106 and has lateral edges 107 and 108 approximately equidistantfrom the respec tive lateral edges 109 and 110 of the active portion106. The lateral ends of the end portion 100 are formed to flanges 111and 112 which extend outwardly of the stacked assembly and extend fromthe main section of the end portion 100 at approximately right anglesand from a pair of sharply defined lines 113 and 114 which arecontinuous with respectively the lateral edges 107 and 108. The flangesterminate in a plane extending transversely of the longitudinal axis ofthe bimetal member, which plane passes through the line 103.

the flange lengths theactive length of the bimetal member may beconveniently adjusted and the deflection of the bimetal member andtherefore the time delay controlled. The off-set intermediate portion104 is in a sense another flange relative to the end portion 100 and assuch precludes cross-bowing of the secured portion 100, therebyprecluding variations in the activity of the intermediate and majorportions due tointer-dependence of warping effects about mutuallyperpendicular axes. The portions 104 and 106 are subject tocross-bowing; how-v ever, as they are not restrained the cross-bowingeffect is uniform. It is principally the secured portion 100 which issubject to non-uniformities due to non-uniformitics in the securingmeans as explained hereinabove, but cross-bowing of portion 100 isprecluded by flange-like restraining action of portion 104. a

ator 58 is provided with a pair of mica spacers 66 and 68 disposed oneach side thereof. The heater 30, which may be made of Nichrome wire, iswrapped in several turns around the mica spacers 66 and 68 and itsends'are connected by means of leads 70 and 72 which are weldedrespectively onto the upper ends of the N0. 3 and No. 2

pins.

The connections 31 comprise the strip 49 and the compensator 48 whichtowards its upper end is bent laterally inwardly at approximately aright angle to form a bimetallic arm 74 integral with the maincompensating portion 48. As is most clearly shown in Fig. 5, arm 74 isbifurcated towards its free end so as to form a pair of fingers 76 and78 separated by a rectangular opening. Fingers 76 and 78 are provided attheir lower surfaces with-V-shaped notches which lend a knife-edgepivotal support to the armature 32. Said armature 32 is made of a thinsheet of planar metallic material, preferably copper for goodconductivity, to the form of a U-shaped yoke with the upper ends of thestems of the U located within the notches in the member 74 and extendingdownwardly thereof approximately in parallel relation to the actuatorand compensator. The U is completed by an interconnecting base portiononto whose sides are mounted the movable contacts 34 and 36. The portion80 is apertured above the contacts 34 and 36 and the lower end of aspring 82 is hooked through this aperture whereas its upper end ishooked onto the .screw 64 adjacent the screw-head. The axis of thespring 82 is disposed substantially in the plane of the yoke 32. Thescrew 64 may be adjusted to vary the throw-over position of the spring82 thereby controlling the timedelay of the relay. Although the yoke issubject to compression it remains substantially planar throughout therange of operating temperature. v p V The switching means described is asnap-action mechanism as the armature or yoke 32 has no stable positionin which neither of the fixed contacts 26 and 38 is engaged. In'theparticular arrangement described the spacing of contacts 26 and 38 isselected to provideone stable position absent heating of the heater 30,namely the normal position in which there is. electrical continuitybetween pins land 4 and pin 5. Continuity is provided by the connections28 which include the bar 44 to which the pin 1 is welded, then bycontacts 26 and 36 and yoke 32, then by the support member 74 and thecompensator 48 integral therewith, then by the bar 49 to the No. 5 pinwelded thereto.

Actuator and compensator are arranged to warp with reference tosupporting structure in a counterclockwise direction responsive to atemperature increase and in a clockwise direction responsive to atemperature decrease. The actuation of the yoke 32 depends only onrelative displacement of the bimetallic members so that no switchingtakes place unless the heater 30 is energized by passage of currenttherethrough. In fact switching does not take place immediately butafter a time delay subsequent to initial energization, i. e. after theheater 30 has heated sufficiently to cause the actuator to warpsutficiently to move the spring 82 overcenter with respect to the yokefulcrum point thereby causing the yoke 32 to snap over" and engagecontact 38.

Because of the constructional features hereinbefore described,variations in time delay from relay to relay have been greatlyminimized. Another beneficial efiect of the improved relay structure hasbeen minimization of hysteresis efiects in cycling a given relay throughits intended ambient temperature rating.

It should be understod that the preceding specification has beenpresented as an example of the invention and not as a limitationthereof, reference being had to the appended claims rather than to thepreceding specification to determine the scope of the invention.

What is claimed is:

1. A thermal time delay relay having a high degree of uniformity intemperature response, comprising a base structure, an actuatorbimetallic member and a compensator bimetallic member each of stripform, each of said members having an end portion secured to saidstructure, an intermediate portion extending from said end portion froma first sharply defined line and laterally and in off-set relation tosaid end portion, and a major active portion extending from saidintermediate portion from a second sharply defined line and in off-setrelation to said intermediate portion, the intermediate portion of eachmember being substantially narrower than the active portion thereof,said end portions being substantially non-responsive to temperaturechanges and the first sharply defined line of each bimetallic memberdefining a uniform fulcrum line for warping of the respective member,said relay further comprising switching means operatively related tosaid active portions and responsive to temperature differencetherebetween, and a heater disposed in proximity to the active portionof said actuator for causing warping thereof about its said fulcrum lineand operation of said switching means after a time delay.

2. A thermal time delay relay having a high degree of uniformity intemperature response, comprising a base structure, an actuatorbimetallic member and a compensator bimetallic member each of stripform, each of said members having an end portion secured to saidstructure that is provided with two flanges extending from said endportion respectively from first and second sharply defined lines andapproximately at right angles, an intermediate portion extending fromsaid end portion from a third sharply defined line and laterally and inoff-set relation to said end portion, and a major active portionextending from said intermediate portion from a fourth sharply definedline and in ofi-set relation to said intermediate portion, said endportions being substantially non-responsive to temperature changes andthe third sharply defined line of each bimetallic member defining auniform fulcrum line for warping of the respective member, said relayfurther comprising switching means operatively related to said activeportions and responsive to temperature difference therebetween, and aheater disposed in proximity to the active portion of said actuator forcausing warping thereof about its said fulcrum line and operation ofsaid switching means after a time delay.

3. A relay as specified in claim 1 wherein the intermediate portion of abimetallic member has lateral edges that are approximately equidistantfrom respective lateral edges of the active portion of said member andwherein the end portion of said member is provided with a pair offlanges each extending from said end portion from a sharply defined linesubstantially continuous with a lateral edge of said narrowerintermediate portion and at approximately a right angle.

4. A relay as specified in claim 2 wherein the intermediate portions ofthe bimetallic members extend towards one another from respective endportions.

5. A relay as specified in claim 3 wherein the intermediate portions ofthe bimetallic members extend to wards one another from respective endportions.

6. A relay as specified in claim 1 wherein the intermediate portions ofthe bi-metallic members extend towards one another from respective endportions.

References Cited in the file of this patent UNITED STATES PATENTS2,288,640 Palus July 7, 1942 2,574,869 Green Nov. 13, 1951 2,593,812Turner Apr. 22, 1952 2,644,874 Miller July 7, 1953 2,658,975 ZuckermanNov. 10, 1953 2,689,288 Wells Sept. 14, 1954 2,693,518 Bower Nov. 2,1954 OTHER REFERENCES Eureka, Thermal Time Delay, pages 1-2, page 1relied upon; August 12, 1953.

